Duo to the fact that Kinmen county is an isolated island,landfill is the original way of handling waste. The lack of waterproof, waste leachate treatment facilities, and groundwater monitoring wells ate common situations for earlier simple landfills in this county. These are potential problems for groundwater pollution that is worth concern. Hence, groundwater hydrogeology of the six closed landfills were investigated in this project in order to speculate the level and scope of groundwater pollution. The main tasks of this project were to collect basic information about these closed landfills including the past, hydrogeological references, and historical trend of groundwater hydrology. Based on the information, standard monitoring wells were established, and groundwater quality testing was made for each landfill. The feasible strategy of managing groundwater pollution risk was mapped out. The prevention and improvement of groundwater pollution were planned for these six closed simple landfills according to the results of water quality testing to secure groundwater quality and safe drinking water. From the results of groundwater quality testing of each landfills, total dissolved solids, ammonia nitrogen, nitrate and total organic carbon (TOC) were common categories that exceed second monitoring standards; number of E. coli exceeding drinking water standard occurred in some of the landfills as well. Besides, both testing values of eight heavy metals and volatile organic compounds (VOCs) were below second monitoring and control standards.